Add Workspaces feature for clipboard isolation

[naman-ajmera]

Summary

Adds a Workspaces feature to Maccy that lets users organize clipboard history into separate, isolated workspaces. This prevents cross-project clipboard pollution — items copied in one workspace never appear in another.

What it does

• Clipboard items are stored per-workspace; only the active workspace's items are shown
• Workspace tabs appear at the top of the popup for quick switching
• Full CRUD: create ("+"), rename (double-click tab or context menu), delete (context menu)
• A "Default" workspace is automatically created on first launch
• Existing clipboard items are migrated into the Default workspace seamlessly
• Workspace management is also available in Settings > Workspaces
• clearOnQuit only clears the active workspace, preserving other workspaces' data

What it doesn't do (current limitations)

• No drag-and-drop reordering of workspace tabs (sortOrder exists in the model for future use)
• No "All Items" global view — always scoped to active workspace
• No moving items between workspaces after copy
• Maximum of 10 workspaces (enforced at data layer and both UIs)

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Reviewer Guide

New files (4)

File	Purpose
Maccy/Models/Workspace.swift	SwiftData @Model — id, name, createdAt, sortOrder, items relationship
Maccy/Observables/WorkspaceManager.swift	Singleton managing workspace CRUD, active workspace persistence, and switching
Maccy/Views/WorkspaceTabsView.swift	Horizontal tab bar in the popup — tap to switch, double-click to rename, context menu for delete, "+" to add
Maccy/Settings/WorkspaceSettingsPane.swift	Settings pane for workspace management (list, add, rename, delete)

Key changes to existing files

File	What changed	Why
Maccy/Models/HistoryItem.swift	Added workspace: Workspace? relationship with inverse: \Workspace.items	Links each clipboard item to exactly one workspace
Maccy/Storage.swift	Registered Workspace.self in ModelContainer; added ensureDefaultWorkspace()	Creates Default workspace on first launch and migrates orphaned items
Maccy/Observables/History.swift	load(), findSimilarItem(), clear(), clearAll() scoped to active workspace; new clearEverything()	All history operations respect workspace boundaries
Maccy/Observables/AppState.swift	Added workspaceManager, isPopoverEditing; registered Workspaces settings pane	Central state for workspace access and rename-popover coordination
Maccy/Observables/Popup.swift	Added workspaceTabsHeight; updated preferredHeight() and resize()	Popup height calculation accounts for workspace tabs
Maccy/Views/KeyHandlingView.swift	selectCurrentItem returns .ignored when isPopoverEditing	Prevents Enter key from selecting a clipboard item while user is renaming a workspace
Maccy/Views/ContentView.swift	Inserted WorkspaceTabsView() between header and history list	Renders workspace tabs in the popup
Maccy/AppDelegate.swift	Calls ensureDefaultWorkspace() + WorkspaceManager.shared.load() at launch; clearOnQuit uses clearEverything()	Bootstrap workspaces before clipboard starts; scoped quit-time clearing

Design decisions worth understanding

1. Workspace identity via stable UUID — not persistentModelID.hashValue. The active workspace ID is persisted in Defaults as a UUID string and restored across launches.

2. SwiftData inverse: on one side only — HistoryItem.workspace declares inverse: \Workspace.items; Workspace.items has @Relationship(deleteRule: .nullify) without inverse. This follows SwiftData documentation to avoid conflicts.

3. #Predicate and static properties — #Predicate macros cannot reference static properties directly. Storage.ensureDefaultWorkspace() captures Workspace.defaultName into a local variable before use in the predicate.

4. clearEverything() fetches from DB directly — At quit time, History.all may not be loaded. The method fetches items matching the active workspace ID from storage rather than relying on in-memory state.

5. findSimilarItem is workspace-scoped — Prevents a duplicate in Workspace A from removing an identical item in Workspace B. This is critical for workspace isolation.

6. Per-method @MainActor — WorkspaceManager uses @MainActor on individual methods (not the class) to match the codebase pattern seen in other observables.

7. Rename popover coordination — A single .onChange(of: showRenamePopover) drives appState.isPopoverEditing, which KeyHandlingView checks to avoid swallowing Enter during rename.

8. Localization pattern — Popup views use bare keys in Localizable.strings; settings panes use tableName:-scoped .strings files (WorkspaceSettings.strings). This matches the existing codebase convention.

9. clear() / clearAll() refactored — Replaced context.delete(model:) bulk deletes with per-item deletion loops. The bulk API deleted across all workspaces; per-item deletion respects workspace scope since History.all only contains active workspace items.

[naman-ajmera]

#1408